This invention relates to an engine control system that breaks the torque lock typically found in a transmission with engaged gears, allowing the transmission to be moved to neutral without actuating the clutch.
A manual transmission typically slides a clutch collar relative to different gears to engage one of the gears. To complete a shift, typically an operator or the system must first move the gear that is presently engaged out of engagement to a neutral position. In some heavy vehicle transmissions, the movement out of engagement is performed by a hydraulic piston, also known as a "shift-by-wire" system.
When the transmission is engaged and rotational drive is being transmitted from the engine to the transmission, there is a large torque load, or "torque lock," holding the gears and the clutch collar together at a particular axial position. This torque load makes it quite difficult, if not impossible, to move the clutch collar out of engagement without somehow reducing the torque load.
To this end, vehicles with manual transmissions have historically been equipped with clutches. An operator actuates the clutch which breaks the coupling between the engine output shaft and the transmission output shaft. The torque load goes to zero, and the operator is able to move the gear out of engagement. As an alternative, control systems have been developed which estimate the transmission output torque and the engine torque and then adjust the engine torque until it matches the transmission output torque. When the torques match, the torque load is zero and a shift may be made without clutching or manipulating the accelerator or brakes for a "clutchless" shift.
Many of these systems have "dithered" the engine torque up and down about the estimated transmission output torque so that the engine torque will eventually equal the transmission output torque. Control systems that utilize dithering require that the engine torque be fluctuated. Therefore, it is desirable to provide a vehicle drive system that utilizes a control system which provides smooth shifts.